I have about 25 niche sites, of which organic traffic is about 80%. Of that, appx 65% is Google. So far, in aggregate, I'm seeing about 15% "not provided".
Most of these sites are ranking for long-tail keywords, and that info is - was - a significant focus of new content and anchor text.
What am I doing about it? Not much I can do, other than renew my efforts at non-organic traffic generation.